1. Field of Invention The present invention relates to antennas and more particularly to an improved ultra-wideband dipole antenna mounted in a wireless communication device (e.g., cellular phone or PDA).
2. Description of Related Art
Wireless communication has known a rapid, spectacular development in recent years. Also, requirements for quality and performance of antenna mounted in a wireless communication device (e.g., cellular phone or PDA) are increased. In addition to the requirement of miniature antenna, multiple frequency band or ultra-wideband feature is also necessary. For many types of newly developed wireless communication devices, having an ultra-wideband antenna is critical for high speed wireless transmission of image data or large amount of data.
A conventional dipole antenna is shown in FIG. 1 and comprises an inner metal conductor 13 having a feed point location 131 at one end thereof, a coaxial conductor 14 having a central conductor 141 electrically connected to the feed point location 131 to form a positive terminal of the antenna, and a metal sleeve 12 connected to an outer grounding cylinder 142 of the coaxial conductor 14 to form a negative terminal of the antenna.
The prior dipole antenna is applicable for a single frequency band operation only and has a bandwidth about 10% to 12% of central frequency of resonance. For example, the dipole antenna operates in a single frequency band in a wireless LAN having a frequency 2.45 GHz and has a bandwidth about 250 MHz. As such, the prior dipole antenna does not meet the requirements for multiple frequency band or ultra-wideband applications. Thus, the need for improvement still exists in order to overcome the inadequacy of the prior art.